1. Field of the Invention
The present invention relates to an electrolytic cleaning method and an electrolytic cleaning solution for a stamper. The present invention particularly relates to an improved electrolytic cleaning method and an improved electrolytic cleaning solution for cleaning a stamper by electrolytically degreasing it.
2. Description of the Prior Art
Stampers, i.e., masters used for duplicating information recording disks such as LP records, optical disks and the like, are generally produced by the following process:
A glass matrix is first polished, and a photosensitive resin film is then coated on the polished surface thereof. A desired fine pattern is formed by optical etching, and a film of a metal such as nickel is then provided on the fine pattern surface. Building-up is then effected by electroplating until a desired- thickness is obtained, and the thus-formed plate is then separated from the glass matrix to form a stamper.
Since the photosensitive resin film remains on the surface of the stamper, however, the resin film must be removed.
Methods used for removing such a film include an electrolytic degreasing cleaning method for electrolytically degreasing by using a usual alkali electrolytic cleaning solution which is a mixed solution containing an alkali and a surfactant (for example, an alkali concentration of about 1%), an ultrasonic cleaning method for cleaning by using ultrasonic waves in an organic solvent and combination of the two cleaning methods.
In a method known as the electrolytic degreasing cleaning method, electrolysis is effected by using as a cathode a stamper (made of nickel), which is suspended by an electrode jig made of copper or stainless steel in an alkali electrolytic degreasing cleaning solution, and as an anode the opposite electrode plate made of stainless (refer to Japanese Patent Laid-Open No. 62-214535). In this method, the solubility of the photosensitive resin film remaining on the surface of the stamper in an alkali is utilized for dissolved the resin film, and the physical function of the occurrence of a large quantity of hydrogen gas is utilized for removing it.
In recent years, the use of information recording disks as optical disks, from which recorded information is optically extracted, has been rapidly advanced in various fields, apart from conventional LP records. In such optical disks, the width of a groove for recording information is 0.5 .mu.m which is 1/100 of 50 .mu.m of LP records.
On the other hand, the fine particles remaining on the stamper, which is used for duplicating disks and cleaned by one of the above various cleaning methods, have a size of 1 to 10 .mu.m.
Since a conventional stamper used for duplicating LP records (or for analogue) has an information recording groove having a width of about 50 .mu.m, therefore, the remaining fine particles have little effect on the stamper, and a sufficient degree of cleaning can be obtained by the conventional cleaning methods.
However, since a stamper for duplicating optical disks (or for digital) has an information recording groove having a width of about 0.5 .mu.m, information recording is fatally affected even by fine particles of 1 .mu.m. The stamper for duplicating optical disks must be cleaned with a degree of cleaning which is significantly higher (residue: 1/100 or less) than that of cleaning of the stamper used for duplicating LP records. Such a high degree of cleaning cannot be easily attained by the above-described conventional electrolytic degreasing cleaning method, ultrasonic cleaning method and the like.